Traditionally, two types of legacy telecommunication networks have been developed. The first type of legacy network is connection oriented and is used for the transport of narrow band voice traffic, typically carried in TDM frames. Such networks comprise for example synchronous or plesiochronous networks. The second type of legacy network is connectionless in nature and is used for the transport of broad band packet or cell-based data traffic. Such packet traffic includes for example Internet protocol (IP) traffic. There is currently a drive towards unified networks which provide end to end transport for both voice and data services, and to this end the use of asynchronous transport has been introduced. This of course introduces the problem of supporting different protocols over a common network.
Asynchronous Transfer Mode (ATM) is the technology specified by the ITU-T as a broadband network technology suitable for all applications. For Internet protocol traffic however, ATM has proven to be less than fully effective at supporting Layer 3 routed applications, such as routed virtual private networks. This has led the IRTF (Internet Research Task Force) to specify multi-protocol label switching (MPLS) as a technology which inherits the desirable characteristics of ATM but is better matched to the Internet protocol. In particular MPLS provides a frame merge function in which data frames received from multiple sources are captured and sent out with a common label. This is required for the support of Internet Protocol Layer 3 Routed services. Service providers would ideally prefer a single network technology to support all of the services that they provide as this would achieve the lowest possible operational cost.
A particular problem with the introduction of a multi-service network is that of accommodating the various transport protocols and, in particular, that of providing end to end quality of service guarantees for high priority traffic such as voice. In particular, there is a need to provide a network that can carry both data and voice traffic at a local, national and international level while utilising a common transport protocol. A further problem with such a network is that of real time management of the virtual public/private networks that are established within the network. At present, each VPN manager requires a detailed knowledge of the network topology. In a large network this is a very significant operational task.